Electromagnetic relay

Abstract

The electromagnetic relay includes a fixed terminal, a fixed contact connected to the fixed terminal, a movable contact piece moving in an opening direction and a closing direction with respect to the fixed terminal, a movable contact connected to the movable contact piece and being arranged to face the fixed contact, a coil generating an electromagnetic force to move the movable contact piece, and a drive circuit controlling a current to the coil. The drive circuit increases the current at a first increase rate in a first period that includes a period from a start time when the current starts to flow in the coil to before a contact time point at which the movable contact contacts the fixed contact. The drive circuit increases the current at a second increase rate larger than the first increase rate in the second period that includes a period after the contact time point.

The invention claimed is: 
     
       1. An electromagnetic relay, comprising:
 a fixed terminal; 
 a fixed contact connected to the fixed terminal; 
 a movable contact piece configured to move in an opening direction and a closing direction with respect to the fixed terminal; 
 a movable contact connected to the movable contact piece and arranged to face the fixed contact; 
 a coil configured to generate an electromagnetic force to move the movable contact piece; and 
 a drive circuit configured to control a current to the coil, 
 wherein 
 the drive circuit is configured 1) to increase the current at a first increase rate in a first period prior to the movable contact contacting the fixed contact, the first period beginning when the current starts to flow in the coil; 2) in a second period subsequent to the movable contact contacting the fixed contact, to increase the current at a second increase rate that is larger than the first increase rate; and 3) in a third period subsequent to the second period, to maintain the current to the coil at a current value larger than a current value during the first period. 
 
     
     
       2. The electromagnetic relay according to  claim 1 , wherein the drive circuit is configured to reduce the current to the coil in a fourth period, subsequent to the third period, to a current value smaller than the current value in the third period. 
     
     
       3. The electromagnetic relay according to  claim 1 , wherein the first period is longer than the second period. 
     
     
       4. The electromagnetic relay according to  claim 1 , further comprising a contact voltage detection unit configured to detect a voltage at the movable contact and the fixed contact,
 wherein the drive circuit is configured to detect the movable contact contacting the fixed contact based on the voltage detected by the contact voltage detection unit. 
 
     
     
       5. The electromagnetic relay according to  claim 4 , wherein the drive circuit starts the second period based on the voltage detected by the contact voltage detection unit. 
     
     
       6. The electromagnetic relay according to  claim 1 , further comprising
 a movable mechanism connected to the movable contact piece; and 
 a movable iron core connected to the movable mechanism and configured to be moved by the electromagnetic force generated from the coil, 
 wherein the first period includes a period from the time at which the current starts to flow in the coil to a time when the movable iron core starts to move. 
 
     
     
       7. An electromagnetic relay, comprising:
 a fixed terminal; 
 a fixed contact connected to the fixed terminal; 
 a movable contact piece configured to move in an opening direction and a closing direction with respect to the fixed terminal; 
 a movable contact connected to the movable contact piece and arranged to face the fixed contact; 
 a coil configured to generate an electromagnetic force to move the movable contact piece; 
 a drive circuit configured to control a current to the coil; and 
 a contact voltage detection unit configured to detect a voltage at the movable contact and the fixed contact, 
 wherein 
 the drive circuit is configured 1) to increase the current at a first increase rate in a first period prior to the movable contact contacting the fixed contact, the first period beginning when the current starts to flow in the coil; and 2) in a second period subsequent to the movable contact contacting the fixed contact, to increase the current at a second increase rate that is larger than the first increase rate, the drive circuit further being configured to detect the movable contact contacting the fixed contact as part of a transition from the first period to the second period based on the voltage detected by the contact voltage detection unit. 
 
     
     
       8. The electromagnetic relay according to  claim 7 , wherein the drive circuit starts the second period based on the voltage detected by the contact voltage detection unit.